Move viewport actions into an ApplyScroll callback.

third_party/WebKit/Source/core/dom/Document.h

Index: third_party/WebKit/Source/core/dom/Document.h
diff --git a/third_party/WebKit/Source/core/dom/Document.h b/third_party/WebKit/Source/core/dom/Document.h
index 646af18ae3e9d41e96803f69705f72f47eea5de7..2b75409efc6abc076c963224935bc95093f9813f 100644
--- a/third_party/WebKit/Source/core/dom/Document.h
+++ b/third_party/WebKit/Source/core/dom/Document.h
@@ -1162,6 +1162,13 @@ private:
 
     RawPtr<OriginTrialContext> createOriginTrialContext() override;
 
+    // Installs the viewport scrolling callback (the "applyScroll" in Scroll
+    // Customization lingo) on the root scrollingElement. This callback is
+    // responsible for viewport related scroll actions like top controls
+    // movement and overscroll glow as well as actually scrolling the root
+    // viewport.
+    void updateViewportApplyScroll();
+
     DocumentLifecycle m_lifecycle;
 
     bool m_hasNodesWithPlaceholderStyle;
@@ -1267,6 +1274,7 @@ private:
     Timer<Document> m_updateFocusAppearanceTimer;
 
     Member<Element> m_cssTarget;
+    Member<Element> m_oldScrollingElement;

[tdresser, 2016/04/05 19:31:12]

Add a comment indicating why this can't be a WeakMember.

[bokan, 2016/04/06 15:21:01]

Actually, I think it can and should. Changed to WeakMember.

[bokan, 2016/04/07 00:39:14]

Forgot to remove this comment after pondering the implications in
Document::UpdateViewportScrollCallback. Comment added.

 
     LoadEventProgress m_loadEventProgress;